Introducing Fiddler

What is Fiddler?

Fiddler is a Web Debugging Proxy which logs all HTTP(S)
traffic between your computer and the Internet. Fiddler allows you to
inspect traffic, set breakpoints, and "fiddle" with incoming or outgoing data.
Fiddler includes a powerful event-based
scripting subsystem, and can be extended using any .NET language.

Fiddler is freeware and can debug traffic from virtually
any application that supports a proxy,
including Internet Explorer, Google Chrome, Apple Safari, Mozilla Firefox, Opera, and thousands more.
You can also debug traffic from popular devices like
Windows Phone, iPod/iPad, and others.
To debug
applications you've written in Java, .NET, or using WinHTTP, see this page.